38 



NATURE 



\_Nov. 14, 1889 



from the belief that methods which involve working at 

 high temperatures are necessarily inaccurate ; but the 

 school of Ste. Claire-Deville has shown that they are not, 

 and there are signs among us that our traditional love for 

 the study of metals is reviving. Of course it cannot be 

 that chemists and physicists are afraid "that science will 

 be degraded by being applied to any purpose of vulgar 

 utihty/' for I trust that I shall at least have shown that 

 the empire over matter, and the true advancement of 

 science, which I suppose is the object of all research, may 

 be as certainly secured in the field of metallurgy as in 

 any other. 



PROF. WEISMANN'S " ESSA YS." 



■pROF. WEISMANN'S suggestions are, with reason, 

 -*■ universally recognized as being most important and 

 valuable ; nevertheless certain questions treated of by him 

 seem to me to require further solution, and at present to 

 constitute difficulties which oppose themselves to an 

 entire acceptance of his hypotheses. 



Death in the Metazoa is, according to him, due (new 

 translation. Clarendon Press, p. 21) to the cells of their 

 tissues having ceased to be able to reproduce themselves — 

 in " the limitation of their powers of reproduction." Such 

 a cessation may be an inevitable result of an excessive 

 amount of work or efficiency on their part, and "the 

 advantages gained by the whole organism " might, as he 

 says (p. 61), " more than compensate for the disadvantages 

 which follow from the disappearance of single cells." 



But granting all this, how did such a process begin 1 

 Some Metazoon must have been the first to die through 

 this failure of reproduction in its component tissue-cells. 

 Yet if the Protozoa were, and are (as Prof. Weismann re- 

 presents), naturally immortal, the first Metazoa must have 

 been entirely composed of immortal cells, and therefore 

 themselves potentially immortal. Granted that cell- 

 aggregations become every now and then accidentally 

 dissolved, that would be " accidental death." Why should 

 natural death arise, and, if it did, what advantage could 

 ensue from the failure of cell-reproduction .'' It could not 

 benefit the race, because as yet there was no race, but 

 only individual clusters of naturally immortal cells which 

 had happened to divide imperfectly. The Professor tells 

 us (p. 29) it is " conceivable that all cells may possess the 

 power of refusing to absorb nutriment, and therefore of 

 ceasing to undergo further division."' But how and why 

 should a cell begin, for the very first time, to practice this 

 abstinence ? That it should do so, is, of course, like 

 many other things " conceivable," but to my judgment it 

 does not appear credible. Of course when once we have 

 a race of mortal organisms propagating by germ cells, it 

 is easy enough to understand how such a race would be 

 benefited by the death of the " useless mouths " belong- 

 ing to it, and therefore by the cessation of the tissue- 

 reproduction which leads to such death. The difficulty 

 lies in the natural death of the very first Metazoa which 

 ever lived. Here, as in so many cases, it is " the first 

 step " which tries us. How, from this perennial race of 

 microscopic immortals, are we to obtain our first Metazoon 

 naturally mortal ? 



By the hypothesis, each component cell consists of a 

 form of protoplasm which has the power of growing and 

 dividing. It is not easy to see how the mere coalescence 

 of such cells can lead any one, or any set, of such cells 

 to acquire an altogether new power — that of reproducing 

 the whole complex organism of which it has come to be 

 a part? The Professor tells us (p. 27) that probably 

 " these units soon lost their primitive homogeneity. As 

 the result of mere relative position, some of the cells 

 were especially fitted to provide for the nutrition of the 

 colony, while others undertook the work of reproduction." 

 Referring to M agosphcpra planuln, he snys (p. 75) : — 



" Division of labour would produce a differentiation of the 

 single cells in such a colony : thus certain cells would be set 

 apart for obtaining food and for locomotion, while certain 

 other cells would be exclusively reproductive." But how 

 can the fact of a cell happening to fall into a position 

 "especially fitted" for the performance of a certain func- 

 tion, lead to its performing this function ? Supposing 

 that the physical influences of the environment have 

 modified the arrangement, or cohesion, size, or number of 

 molecules in a cell, or modified their molecular motions, 

 how can such influences give it a power, not of repro- 

 ducing its thus " acquired " characters, or the characters 

 of the cell before it becomes thus differentiated, but of 

 reproducing the whole organism whereof it forms a part 't 

 Is it credible that any impacts and reactions thus occa- 

 sioned should produce so marvellous a result .^ I do not 

 know any phenomena in Nature which could warrant us 

 in entertaining such a belief. 



Of course, if we were dealing with races of creatures 

 sexually reproduced, it is conceivable enough that, out of 

 multitudinous, indefinite, minute accidental changes in the 

 arrangements of the molecules of their germs, favourable 

 arrangements might be selected in the struggle for life. 

 But we are here concerned with nothing of the kind, but 

 with the first appearance of the earliest Metazoa repro 

 duced. If we meditate on the conditions affirmed by the 

 Professor to have produced that origin, it will, I think, 

 be clear that no hypothesis suggested by him will answei 

 the question how any of the cells of the first coherent 

 colonies came to reproduce, not such cells as their ances- 

 tors (or, rather, the earlier living portions of their very 

 selves) had by countless processes of fission produced, 

 but a whole " cell-colony," such as that whereof they had, 

 by the hypothesis, for the first time come to form a part. 



With respect to the immortality of Monoplastides and 

 the question of death generally, he (the Professor) makes 

 various remarks which do not appear to be satisfactory. 

 The process of spontaneous fission, he says (p. 25), 

 " cannot be truly called death. . . Nothing dies, the body 

 of the animal only divides into two similar parts possessing 

 the same constitution." Where such a perfect similarit\ 

 exists we n;ay say not only that there is no death, but also 

 that there is no birth. In some of the Monoplastides, how 

 ever, the relationship between parent and offspring does 

 exist, but this, of course, need not necessarily involve 

 death ; as we see in higher species and in our own. But 

 the fact that death does not take place during, or soon 

 after, fission, does not prove that death never naturally 

 occurs at all, and that the cell can balance its metabolism 

 indefinitely. Very likely it may be able so to do, but this 

 can hardly be affirmed to be an absolute certainty. What 

 may be certainly affirmed is that reproduction by fission 

 does not entail death to the degree that sexual reproduction 

 entails it. But reproduction by gemmation may equally 

 fail to entail death ; as we see in the parthenogenetic 

 Aphis and many Hydrozoa. 



In Eiig/ypha we can, as Prof. Weismann admits (p. 64), 

 recognize the daughter cell (which is for a time without a 

 nucleus, and we also find a very marked distinction 

 between the segments of transversely dividing Infusorians ; 

 where one has to form a new mouth and the other a 

 new anus. 



After all that can be urged, then, in contrasting the 

 multiphcation by fission of Monoplastides with reproduc- 

 tion in the life- cycle of Polyplastides, there seems to me 

 to be more of a true reproductive process in the former 

 than the Professor is disposed to allow. In some Heliozoa 

 and Ciliata we have all the complexity of indirect nucleus 

 division by karyokinesis, while in Euglypha we have cell 

 division without any antecedent separation of the nucleus- 

 into two parts. Of course it is easy enough to understand 

 how a mere augmentation in bulk may overcome cohesion,, 

 how internal molecular arrangement may cause cleavage 

 along definite lines, and, perhaps, even how such cleavage- 



